The URL masking is a method that allow you to mask certain part of your website’s address.
For example, when someone opens up:
https://yourdomain.com/something
The actual content that will be displayed can be the one under:
https://yourdomain.com/something/else
Although the URL in the visitor’s address bar will still remain http://yourdomain.com/something.
You can achieve this by adding rules similar to the ones below into your website’s .htaccess file:
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RewriteEngine On
RewriteRule ^something/?$ /something/else/
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Make sure to substitute something and else which the actual directories that you are using on your website.